This invention relates to an exhaust silencing means for marine propulsion more particularly to an improved silencing system for an internal combustion engine.
As is well known, it is desirable if not necessary to silence the exhaust gases issuing from the exhaust ports of an internal combustion engine before they are discharged to the atmosphere. A wide variety of devices have been proposed for silencing the exhaust gases. To a large extent, the noises of the exhaust gases result from the pulsations which occur in the exhaust system due to the opening and closing of the exhaust ports. It has been proposed to silence the exhaust gases by providing a variable volume chamber that communicates with the exhaust passage and in which a floating piston is supported so as to dampen these pulsations. However, the device of this type previously proposed has not been fully effective. One of the main reasons for this is that the exhaust gases may freely pass through the floating piston and as a result the damping operation of the piston is not particularly effective.
It is, therefore, a principle object to this invention to provide an improved arrangement for silencing the exhaust gases of an internal combustion engine by utilizing a variable volume chamber than communicates with the exhaust system and which is defined at least in part by a flexible diaphragm so as to improve the silencing efficiency.
In conjunction with outboards motors, a common application of internal combustion engines, the problem of exhaust silencing is particularly acute. The reason for this is that the outboard motor and its contained exhaust system must be extremely compact. Therefore, a wide variety of exhaust silencing devices that are effective in other applications simply cannot be used to any practical extent in such an application.
In addition to the size problem, the outboard motors normally utilize a below the water exhaust gas discharge for assisting the silencing of the exhaust gases under high speed operation. However, the back pressure of such under water exhaust systems is to high in conjunction with low speed operation and hence it has also been proposed to employ above the water exhaust. For the most part, the above the water exhaust system is completely independent of and uses different silencing devices for the exhaust gases than the underwater exhaust gas discharge.
It is, therefore, a still further object of this invention to provide an improved exhaust silencing device for an outboard motor.
It is a further object of this invention to provide an improved exhaust silencing device for an outboard motor that is operative to provide silencing for both the above the water and the below the water exhaust gas discharges.
A type of silencing device which is particularly effective is known as a Helmholtz resonator. This type of resonator is particularly effective in reducing exhaust noises, but operates only at a predetermined frequency range depending upon its volume and the length and size of its tuning neck. It has been proposed to vary the volume of the chamber in order to achieve silencing over a wider range. However, this type of device only operates on the Helmholtz principle.
It is, therefore, a still further object of this invention to provide an improved Helmholtz resonator for the exhaust system of an internal combustion engine which will silence exhaust pulses by means of the Helmholtz principle and in addition by utilizing a variable volume chamber to dampen the pulsations, as aforedescribed.
In conjunction with the use of variable volume chambers for silencing exhaust gases the use of a flexible diaphragm is particularly advantageous. However, the use of flexible diaphragms and particularly those comprised of elastomeric materials is not normally thought to be suited for exhaust systems due to the inability of most elastomers to sustain high temperatures as are present in exhaust gases.
It is, therefore, a still further object of this invention to provide an improved arrangement for employing an elastic diaphragm for silencing the exhaust gases of an internal combustion engine and also a means for cooling the diaphragm.
In connection with certain types of exhaust systems, particularly those found in outboard motors, there is additionally a problem of generating resonance in the exhaust system when large resonant chambers are employed. Such large resonant chambers themselves have their external walls acting as sound generating media. It has, therefore, been proposed to provide some damping arrangement for the movement of such external walls.
In accordance with another feature of this invention, it is an object to provide an arrangement which will dampen the movement of the walls and also provide a damping effect to the pulsations of the exhaust gases.